Every NASDAQ-listed stock — Apple, Facebook, Microsoft, etc. — was halted. As a result, both the index and individual stocks flatlined.

The exchange just reopened for trading at 3:25 PM ET, and shares of all three of those companies are rising, as is the broader index.

Upon opening, NASDAQ declared “self help” against NYSE Arca, a signal that orders should be rerouted to other exchanges because NYSE Arca is having issues processing trades. The BATS Exchange also said it stopped routing orders to NYSE Arca as of 3:39.

NASDAQ said the unprecedented trading halt this afternoon was due to a UTP SIP quote dissemination issue.

(UTP stands for “unlisted trading privileges” and refers to the ability of other exchanges to trade securities listed on the NASDAQ. SIP stands for “securities information processor” and is the system that allows NASDAQ to send quotes for those securities to other exchanges.)